London , England -LRB- CNN -RRB- -- Metropolitan police in London , England , appealed Monday for further information about last month 's death of a man who worked for a British intelligence agency and whose naked body was found in a padlocked duffel bag in his bathroom .

Police also released surveillance camera images of Gareth Williams taken August 15 , about a week before officials discovered his body on August 23 .

In addition , police said they would like help identifying `` a man and a woman , both of Mediterranean appearance , '' between the ages of 20 and 30 and who were seen entering Wiliams ' apartment building late one evening in June or July .

`` This remains a complex unexplained death enquiry , '' Det. Chief Inspector Jacqueline Sebire said in a statement Monday .

Williams worked at Government Communications Headquarters -LRB- GCHQ -RRB- , Britain 's intelligence agency for monitoring communication and keeping government data secret , the agency told CNN . He was widely reported to have been on loan to MI6 , the foreign intelligence service , in London .

The crime scene did not seem to reveal much information .

`` There was no sign of any forced entry to the property , and no signs of disturbance inside , '' police said , adding that robbery did not appear to be a motive .

`` We do not believe there is any property missing from the flat , '' the police statement said . `` There is no suggestion the items within the flat were specifically posed . No drugs , or indications of drug usage were recovered . ''

An August 25 autopsy `` established no obvious cause of death , '' police said .

`` Extensive forensic tests at the flat in Alderney Street and from the samples taken at the post mortem continue , '' police said .

`` Initial indications from the toxicology examinations show no trace of any alcohol or routine or recreational drugs . Testing for any other substance continues . ''

Police believe Williams was last seen alive on August 15 , when surveillance cameras show him shopping in the West End and Knightsbridge areas of London .

He had returned August 11 from a trip to the United States , police said Monday .

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His naked body was found stuffed inside a locked bag in his bathroom

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Victim Gareth Williams was on loan to MI6 , the foreign intelligence service , reports say

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Surveillance video shows him shopping on August 15 , about a week before his body was discovered

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Police say they found no sign of forced entry or robbery